Multi-Stage Compressor

ABSTRACT

A multi-stage compressor for compressing a fluid, the compressor comprising two or more cylinders each having a compression chamber and a piston, so that a fluid in each of the compression chambers can be com-pressed by the associated piston; the cylinders being connected in series such that a fluid entering an inlet of the compressor can be compressed to a first pressure in the compression chamber of a first cylinder and, then, enter into the compression chamber of a second cylinder where the compressed fluid is compressed to a second higher pressure and, before the fluid exits from an outlet of the com-pressor; wherein each piston is driven by one and the same crankpin of the compressor. Furthermore, a method for compressing a fluid, and a system for comprising the multi-stage stage compressor are disclosed.

CROSS REFERENCE TO RELATED APPLICATION

The present patent application is the U.S. national phase entry under 35 U.S.C. 371 of International Patent Application No. PCT/DK2021/050227, filed on Jul. 7, 2021 and claiming priority to Danish patent application PA 2020 00817, filed Jul. 7, 2020, the subject matter of both aforementioned applications are incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

Multi-stage compressors are known for example from U.S. Pat. No. 2,151,825 with multiple cylinders in line driven by a standard crankshaft shaft.

Compressors for generating pressure are known for example from WO07036972A1 which discloses a hydraulic machine with radial cylinders having an improved bearing in the crankshaft, i.e. a machine with radial cylinders fixed to its crankcase, advantageously for pressurised hydraulic liquids, in which the respective connecting rod is coupled with the crankshaft through an improved bearing with rolling friction, so as to reduce the parts worked, to simplify the processing and assembly processes, increasing the mechanical performance of the machine and improving its lifetime.

SUMMARY

The present disclosure concerns a multi-stage compressor for compressing a fluid, the compressor comprising:

-   -   two or more cylinders each having a compression chamber and a         piston, so that a fluid in each of the compression chambers can         be compressed by the associated piston;     -   the cylinders being connected in series such that a fluid         entering an inlet of the compressor can be compressed to a first         pressure in the compression chamber of a first cylinder and,         then, enter into the compression chamber of a second cylinder         where the compressed fluid is compressed to a second higher         pressure before the fluid exits from an outlet of the         compressor.

A first aspect of the present disclosure concerns a multi-stage compressor according to the introduction, wherein each piston is driven by one and the same crankpin of the compressor.

In this way, as the pistons are driven by one and the same crankpin, and therefore each piston does not require its own crankpin, the multi-stage compressor may be made more compact in the axial direction of the compressor i.e. in the direction the crankpin extends.

A multi-stage compressor may be understood as a compressor in which a fluid is compressed to a first pressure in a compression chamber of a first cylinder and this compressed fluid is then at least passed into a compression chamber of a second cylinder where the compressed fluid is compressed even further to a second, higher pressure. The compression chamber of each cylinder may define a stage of compression of the multi-stage compressor. The multi-stage compressor may comprise more than two stages and/or cylinders with compression chambers. The fluid entering the inlet of the compressor may be pre-compressed i.e. the fluid entering the inlet may already be compressed. That is, the fluid entering the inlet of the compressor may be at a pressure above atmospheric pressure. For example, the fluid entering the inlet may be at a pressure of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 bar or more above atmospheric pressure. This can facilitate the generation of fluid compressed to even higher pressures by the compressor.

The fluid may be any suitable fluid, liquid, and/or gas. The fluid may be a compressible fluid.

The crankpin may extend in an axial direction and/or a radial direction of the compressor. The crankpin may rotate about a rotation axis to drive the pistons. The crankpin may be positioned with a distance to the rotation axis. The crankpin may be positioned with a distance to the rotation axis in the radial direction. There may be a distance from a center axis of the crankpin to the rotation axis. The rotation axis may be located outside of a periphery of the crankpin. The rotation axis and the axial direction may be parallel. The crankpin may be attached to a rotatable crankshaft. The crankshaft may extend externally of the compressor housing. The crankshaft may extend in the axial direction of the compressor. The crankshaft may extend beyond the housing of the compressor. The crankshaft of the compressor may be configured such that a drive unit and/or a crankshaft of another compressor may be coupled to it. The rotation axis may be concentric with the crankshaft. A radial direction may extend perpendicularly from the axis of rotation. The crankpin may be cylindrical with a length extending in the axial direction and a crankpin diameter extending perpendicularly to the axial direction. The crankpin may be positioned with a distance “D” from the rotation axis to the center axis and/or periphery of the crankpin of at least 0.1, 0.25, 0,5, 1, 2, 3, 4, 5, or more crankpin radii. The periphery of the crankpin may overlap the rotation axis when looking in a direction parallel to the rotation axis. The crankpin may have an outer diameter that is equal to or larger than a largest outer diameter of at least one and/or two, and/or three, and/or four, and/or five, and/or six or more pistons of the compressor. The crankpin may have an outer diameter that is equal to or larger than a largest diameter of all pistons of the compressor. The crankpin may have a diameter that is equal to or more than 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 times the largest outer diameter of the pistons of the compressor. This may allow shorter pistons to be used and/or may reduce the lever arm acting on the crankpin and potentially thereby on the axis of rotation and/or crankshaft. Reducing the lever arm may reduce the amount of torque required to drive the compressor, whereby the power consumption of the compressor may be reduced and the efficiency increased. At least one, two, three, four, five, six or more pistons may have a substantially constant outer diameter and/or a constant outer diameter. A substantially constant outer diameter and/or constant outer diameter may be understood as the outer diameter being substantially the same and/or the same along the entire length of the piston(s).

At least one, two, three, four, five, six or more pistons may have different piston lengths “L”. The sliding shoes may be substantially identical or identical to each other. The holding rings may be substantially identical or identical to each other. Identical sliding shoes and/or identical holding rings may facilitate the stroke length being defined by the piston length of the associated piston, particularly as the pistons are driven by the same crankpin and/or crankpin bearings. The length “L” of a piston may be a length extending in the radial direction. The length of a piston may extend from a top surface of a top end to a bottom surface of a bottom end of the piston. The diameter of a piston may extend orthogonally to its length. The length of a piston may alternatively be denoted piston length. A stroke length of a piston may be defined as the distance a piston travels in the associated cylinder and/or compression chamber in operation of the compressor. Additionally or alternatively, a stroke length may be a distance a top end and/or a bottom end of a piston travels between the bottom most point of a stroke and the upper most point of a stroke. Additionally or alternatively, a stroke length may be a distance a top end and/or a bottom end of a piston travels between bottom dead center and top dead center.

The term “associated” may be understood as being linked to or directly working together with, potentially in contact with. For example a cylinder may have an associated piston and an associated compression chamber, the associated piston working inside the associated compression chamber. Similarly, a cylinder and/or piston may have an associated seal such as a rod seal for sealing between said piston and said cylinder.

The cylinders may be located about the axis of rotation. The cylinders may extend in the radial direction away from the axis of rotation. The compression chambers may be located within the associated cylinders. The compression chambers may be a hollow spacing within a cylinder in which the fluid is compressed. The hollow spacing may take up a fraction of a total volume of a cylinder. The hollow spacing may be cylindrical. The compressor may comprise at least 3, 4, 5, or 6 or more cylinders. The compressor may comprise 2, 3, 4, 5, or 6 cylinders. If more than two cylinders are present, the fluid may successively enter into and be compressed to a successively higher pressure in the compression chamber(s) of the additional cylinder(s).

The pistons may be cylindrical and/or disc-shaped. The pistons may, in operation, move up and down and/or substantially, substantially only, or only in the radial direction of the compressor and/or in an axial direction of the respective piston or only or substantially only in an axial direction of the respective piston in the combustion chambers and/or cylinders. The pistons may, in operation, oscillate up and down in the combustion chambers and/or cylinders. The pistons may have a diameter or outer diameter, or largest outer diameter “d”, that is smaller than or equal to a diameter or inner diameter of the associated combustion chambers. There may, potentially in operation and/or at standstill of the compressor, be a gap between an inner wall of a compression chamber and a periphery of the associated piston. The piston may, potentially in operation and/or at standstill of the compressor, be distanced by a gap from an inner wall of the compression chamber. The gap may surround an entire periphery of the associated piston. The pistons may extend in the radial direction. The pistons may comprise and/or consist of a solid material. The pistons may comprise and/or consist of a hollow material. A hollow material may be lighter than a solid material whereby efficiency of the compressor may be improved as the inertia of the piston may be reduced and less mass has to be moved to compress a fluid. The pistons may be made of metals, metal alloys, e.g. brass, steel, aluminium or aluminium alloys, bronze, and/or combinations thereof. The pistons may be made of steel with an aluminium core.

An inlet of the compressor may be understood as an entry duct for fluid to enter the compressor. The inlet may enter into the compression chamber of a first cylinder of the compressor i.e. into the first stage of the compressor. The inlet may be understood as a point of entry for fluid into the compressor. Fluid may enter the compression chamber of a first cylinder of the compressor i.e. the first stage of compression of the compressor through the inlet. The inlet may comprise a non-return valve as described herein for preventing fluid from flowing from a compression chamber and outside of the chamber through the inlet. The inlet and outlet of the compressor may be positioned on the same side of the compressor. This may provide easy access to the inlet and outlet.

An outlet of the compressor may be understood as an exit duct for fluid to exit the compressor. The outlet may exit out of the compression chamber of a final cylinder of the compressor i.e. the final stage of compressor. The outlet may be understood as a point of exit for fluid out of the compressor. Fluid may exit the compression chamber of a final cylinder of the compressor i.e. the final stage of compression of the compressor through the outlet. The outlet may comprise a non-return valve as described herein for preventing fluid from flowing from outside of the compression chamber and into the chamber through the outlet.

The crankpin may be located with a distance to the crankshaft i.e. such that there is a distance between a periphery of the crankpin and a periphery of the crankshaft. The crankpin may be located at a point located radially from the axis of rotation of the crankshaft. The crankpin may extend in parallel with the crankshaft. One or more bearings such as e.g. a roller bearing and/or plain bearing may be attached and/or mounted on the crankpin. Two roller bearings may be mounted on the crankpin. The crankpin may be a part separate of the crankshaft. The crankpin may comprise, consist of, and/or be coated with a plain bearing material such as e.g. metals, metal alloys, or polymers e.g. brass, steel, aluminium or aluminium alloys, bronze, PTFE, and/or combinations thereof.

The crankpin and/or one or more bearing(s) positioned on the crankpin may be positioned with a distance from the rotation axis of the crankshaft to a center axis and/or a periphery of the crankpin, this distance potentially being at least 0.1, 0.25, 0,5, 1, 2, 3, 4, 5, or more of a radius of the crankpin. A periphery of the crankpin and/or bearing(s) positioned on the crankpin may overlap the rotation axis. This may reduce the length of a lever arm acting on the crankpin and/or the rotation axis of the crankshaft. Additionally or alternatively, the crankpin and/or bearing(s) may have an outer diameter that is equal to or larger than a largest outer diameter of at least one and/or two and/or three and/or four and/or five and/or six or more pistons of the compressor. Additionally or alternatively, the crankpin and/or bearing(s) may have an outer diameter that is equal to or larger than a largest diameter of all pistons of the compressor. Additionally or alternatively, the crankpin and/or bearing(s) may have an outer diameter that is equal to or more than 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 times the largest outer diameter of the pistons of the compressor. This may allow shorter pistons to be used and/or may reduce the length of the lever arm acting on the crankpin and potentially thereby on the axis of rotation and/or crankshaft. Reducing the length of the lever arm may reduce the torque required to drive the compressor, whereby the power consumption of the compressor may be reduced and/or the efficiency thereof increased. The one or more bearings positioned on the crankpin may alternatively be denoted crankpin bearing(s). The crankpin bearing(s) may drive the pistons of the compressor. The crankpin bearings may be axial-radial bearings such as axial-radial roller bearings.

A lever arm may also be denoted a moment arm. The length of the lever arm acting on the crankpin and/or the rotation axis may be equal to or less than 200%, 190%, 180%, 170%, 160%, 150%, 140%, 130%, 120%, 110%, 100%, 90%, 80%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, or 5% of smallest and/or largest stroke length of the pistons of the compressor. Additionally or alternatively, the length of the lever arm acting on the crankpin and/or the rotation axis may be equal to or less than 90%, 80%, 70%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, or 5% of a piston length of the shortest and/or longest piston of the compressor. The crankpin and/or crankpin bearing(s) may have an outer diameter that is equal to or more than 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5 times a smallest and/or largest stroke length of each piston of the compressor. The crankpin and/or crankpin bearing(s) may have an outer diameter that is equal to or more than 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 times a piston length of the shortest and/or longest piston of the compressor. The technical features in this paragraph may provide a shorter lever arm with the advantages as described above.

The crankshaft may be supported in the compressor housing by one or more crankshaft bearings e.g. plain and/or roller bearings such as described herein. The crankshaft may comprise at least two interconnected shafts. Each shaft may be supported in the compressor housing by one or more crankshaft bearings e.g. plain and/or roller bearings such as described herein. The at least two shafts may be concentric with each other and/or the rotation axis. The at least two shafts may be of equal length and/or diameter. The at least two shafts may be of different lengths. At least one of the at least two shafts may be configured for engaging with a drive unit for driving the compressor. At least one of the at least two shafts may be a driveshaft for driving the compressor. The crankpin may be located between two of the at least two shafts. The crankpin may be mounted eccentrically to the at least two shafts. The crankpin may interconnect two of the at least two shafts. The crankpin may interconnect two shafts by being clamped to the two shafts. The crankpin may interconnect two of the at least two interconnected shafts by being clamped and secured to a respective end of each of the two shafts by a bolt clamp mechanism. The crankpin may be clamped and secured to a respective end of each of the two shafts at respective ends of the crankpin. The crankpin and the at least two shafts may be in one piece. The crankpin and the at least two shafts may be machined from one piece to form a continuous unit.

The compressor may be electrically driven by for example an electric drive unit powered by e.g. battery, solar, wind, wave, nuclear, thermal energy sources, preferably sustainable energy sources. Additionally and/or alternatively, the compressor may be driven by a fossil fuel powered drive unit.

A piston may extend beyond its associated compression chamber and/or cylinder towards the axis of rotation. A total length of a piston in a radial direction may be longer than a total length of the associated compression chamber in the radial direction. A piston at top dead center (TDC) i.e. at the top point of its stroke may extend beyond its associated cylinder towards the axis of rotation. A piston may extend away from and beyond its associated compression chamber and/or cylinder in a direction facing towards the crankpin. A piston at top dead center may extend away from and beyond its associated compression chamber and/or cylinder in a direction facing towards the crankpin. Each cylinder and/or piston may comprise a linear seal such as a piston seal and/or rod seal for sealing between the associated piston and cylinder. The, or one or more, cylinder(s) may comprise one or more rod seals for sealing against the piston. The piston may be the associated piston of the cylinder. For example, the first cylinder and/or a cylinder base of the first cylinder may comprise one or more rod seals for sealing against the associated piston of the first cylinder, and/or the second cylinder and/or a cylinder base of the second cylinder may comprise one or more rod seals for sealing against the associated piston of the second cylinder, and/or a third cylinder and/or a cylinder base of the third cylinder may comprise one or more rod seals for sealing against the associated piston of the third cylinder, and/or a fourth cylinder and/or a cylinder base of the fourth cylinder may comprise one or more rod seals for sealing against the associated piston of the fourth cylinder, and/or a fifth cylinder and/or a cylinder base of the fifth cylinder may comprise one or more rod seals for sealing against the associated piston of the fifth cylinder, and/or a sixth cylinder and/or a cylinder base of the sixth cylinder may comprise one or more rod seals for sealing against the associated piston of the sixth cylinder, and so forth. The piston may comprise one or more linear seals such as a piston ring and/or shaft seal. The seals may be hydraulic and/or pneumatic seals. The cylinder and/or piston may comprise a combination of hydraulic and/or pneumatic seals. A linear seal may be positioned circumferentially in a cylinder or on a piston. A linear seal may be positioned in the circumference of a cylinder and/or compression chamber and/or on the circumference of a piston. The linear seal may be positioned in the cylinder and/or compression chamber adjacent to a tip of a piston at bottom dead center. A tip of a piston at bottom dead center may be located in a cylinder and/or compression chamber with a distance to a cylinder base and/or bottom of an associated compression chamber. A linear seal may be installed circumferentially on a part of a piston positioned within a cylinder and/or compression chamber.

One or more, or all, of the pistons may not comprise any seal such as for example a piston ring or a piston seal, potentially attached to and/or mounted on the piston. In an embodiment no seal is attached or mounted on one or more, or all, of the pistons. Such a seal is typically positioned between an outer diameter of a piston and the inner wall of the associated compression chamber acting to seal therebetween. The movement of a piston being configured such that it does not touch the inner wall of the associated compression chamber in operation and/or during standstill and the provision of a seal such as a rod seal and/or shaft seal which is positioned in the cylinder housing for sealing between the piston and the associated compression chamber may prevent the piston from contacting and/or wearing on and/or damaging the inner wall of the compression chamber and ensure adequate sealing of the compression chamber, particularly towards the crank housing, which may allow the omission of a seal on the piston such as a piston seal and/or piston ring(s). Additionally or alternatively, the compressor and/or one or more pistons and/or one or more cylinders and/or one or more compression chambers and/or one or more sliding shoes and/or the crankpin and/or one or more bearings positioned on the crankpin and/or one or more guide grooves and/or one or more guide elements, and/or one or more rod seal(s) included in the cylinder base may be configured such that, in operation and/or at standstill, at least one or each piston do(es) not or substantially not touch or is/are configured to not or substantially not touch, an inner wall of the associated compression chamber. Additionally or alternatively, the compressor and/or one or more pistons and/or one or more cylinders and/or one or more compression chambers and/or one or more sliding shoes and/or the crankpin and/or one or more bearings positioned on the crankpin and/or one or more guide grooves and/or one or more guide elements, and/or one or more rod seal(s) included in the cylinder base may be configured such that, in operation, at least one or each piston only or substantially only move(s) or is/are configured to only or substantially only move in the radial direction of the compressor. Hereby, frictional losses from the piston(s) moving in the compression chamber(s) may be reduced and/or prevented, which may increase efficiency of the compressor. This may also reduce wear on the inner wall(s) of the compression chamber(s) and/or a periphery, potentially a peripheral surface, of the piston(s), thereby extending service intervals and/or lifetime of the compressor.

A “periphery” may be understood as the outer limits and/or edge of an object. Similarly, a “peripheral surface” may be understood as an outer and/outermost surface of an object. The periphery of an object may substantially coincide or coincide with a diameter and/or outer diameter and/or outermost diameter of the object.

The two or more cylinders may be positioned radially about the rotation axis. The two or more cylinders may be radial cylinders. The two or more cylinders may be equidistantly spaced around the axis of rotation. The two or more cylinders may be equidistantly spaced in the radial direction from the axis of rotation.

The compressor may comprise cooling channels for cooling the cylinders and/or compression chambers. Each cylinder may comprise one or more cooling channels for cooling the cylinder and/or compression chamber. The one or more cooling channels may be interconnected through one or more cooling pipes extending between the cylinders. The one or more cooling pipes may extend externally of the cylinders. The one or more cooling channels and the one or more cooling pipes may form a cooling circuit for cooling the cylinders. Each cylinder may comprise at least one cooling channel with a first direction of flow and at least one cooling channel with a second direction of flow. The second direction of flow may be opposite to the first direction of flow. In this way a circulating flow of a cooling medium may be provided. The two cooling channels of each cylinder may be interconnected with two cooling channels of a preceding and/or a successive cylinder, wherein each cooling channel of each cylinder is interconnected to a respective cooling channel of a directly preceding and/or directly following cylinder through a respective cooling pipe. In a cylinder defining the first or final compression stage, the at least one cooling channel with a flow in a first direction and the at least one cooling channel with a flow in a second direction may be interconnected to form a loop such that a cooling medium flow may circulate through the respective cylinder and to a preceding cylinder.

In an embodiment the multi-stage compressor further comprises at least one supply compressor for supplying compressed fluid at a pressure above atmospheric pressure to the compression chamber of the first cylinder and/or inlet of the multi-stage compressor, wherein the supply compressor and the pistons is driven by one and the same crankshaft as the pistons of the multi-stage compressor. In a development of the previous embodiment the at least one supply compressor is driven by the one and same crankpin as the pistons of the multi-stage compressor.

The supply compressor may be a reciprocating compressor and/or a membrane compressor, and/or a piston compressor. The multi-stage compressor may comprise two, three, four, five, or more supply compressors each supplying compressed fluid at a pressure above atmospheric pressure to the compression chamber of the first cylinder. One or more of the supply compressors may be mounted and/or installed on and/or in and/or inside the multi-stage compressor. The one or more supply compressors may be positioned and/or mounted and/or installed at least partly inside the compressor housing. The one or more supply compressors may operate in parallel. One or more supply compressors may be positioned externally of the multi-stage compressor housing. One or more supply compressors may be positioned circumferentially around the one and the same crankshaft driving the pistons. One or more supply compressors may be positioned outside of the multi-stage compressor housing circumferentially around the one and same crankshaft. Each of the one or more supply compressors may be driven by one and the same second crankpin. The second crankpin may be positioned externally of the multi-stage compressor housing, potentially on the one and same crankshaft driving each piston.

One or more supply compressors may be positioned within an outer periphery of the multi-stage compressor. One or more of the supply compressors may be positioned at least partly within or within the multi-stage compressor housing. One or more of the supply compressors may be attached to respective valve pipe and/or cooling pipes. One or more of the supply compressors may be positioned between, potentially in a spacing between, adjacent cylinders of the multi-stage compressor. One or more, or each, of the supply compressor(s), potentially a respective outlet of each of the supply compressors, may be connected to the compression chamber of the first cylinder, potentially through a respective supply pipe. Each of the supply compressors may be connected to the inlet of the compression chamber of the first cylinder, potentially through an associated respective supply pipe. One or more of the supply pipes may flow into one common pipe and/or manifold before entering the compression chamber of the first cylinder.

Tests show that inclusion of such a supply compressor for compressing air provides an adequate amount of compressed air to the compression chamber of the first cylinder with minimal noise from the supply compressor and minimal impact on the drive unit driving the multi-stage compressor. Equal results are expected for other gases as well as fluids. In an embodiment a separate and individual sliding shoe for engaging with the crankpin is attached to a bottom end of each piston.

In this way the compressor may be quick to assemble as a connecting rod is not required. This may improve efficiency of the compressor as less energy may be lost to overcome inertia of moving parts and/or friction between moving parts. Further, the movement of each piston may be kept independent which may improve design choice and adaptability of the compressor. The bottom end of a piston may be an end opposite a top end of the piston. A top end of the piston may be positioned within an associated compression chamber. A top surface of a top end of a piston may compress a fluid in the associated compression chamber. The bottom end of a piston may be an end of the piston closest to and/or facing the crankpin and/or the axis of rotation. Each sliding shoe may be mounted on the bottom end of an associated piston. Each sliding shoe may be mounted at the bottom end of an associated piston. Each sliding shoe may be attached to an associated piston via a connecting shaft extending through the bottom end of the associated piston and at least one portion of the associated sliding shoe. Each sliding shoe may be detachable from their associated piston. The sliding shoes may be separate parts i.e. individual parts that are not connected to each other. Each sliding shoe may engage with the crankpin and/or a crankpin bearing attached on the crankpin. The sliding shoes and/or a sliding surface of the sliding shoes engaging, or for engaging, with the crankpin and/or crankpin bearing may comprise and/or be coated with and/or consist of a plain bearing material such as metals, metal alloys, or polymers e.g. brass, steel, aluminium or aluminium alloys, bronze, PTFE, and/or combinations thereof. The sliding surface may be shaped form-fittingly to the crankpin and/or a crankpin bearing mounted on the crankpin. The sliding surface may be arc-shaped and/or shaped as part of a circumference of a circle. A sliding surface of a sliding shoe may be a lower and/or bottom surface of a sliding shoe and/or a surface for facing the crankpin and/or a crankpin bearing. A sliding surface of a sliding shoe may be a surface of the sliding shoe for sliding on the crankpin and/or a crankpin bearing. One or more, or each sliding shoe(s) may comprise a sliding surface for engaging with the crankpin and/or a crankpin bearing attached on the crank pin. Said sliding shoe sliding surface may be a part for engaging with the crankpin and/or a crankpin bearing attached on the crank pin of a sliding shoe.

At least one crankpin bearing for engaging with the sliding shoes may be mounted on the crankpin. The crankpin bearing may be circular. The crankpin bearing may be located between the crankpin and the sliding shoes. The crankpin bearing may be a plain bearing, also known as a sliding bearing or slide bearing, or may be a roller bearing, or any other suitable bearing. The sliding shoe may engage with an outer surface of the crankpin bearing. A roller bearing may be understood as a bearing with an inner race and an outer race with rolling elements between the inner race and the outer race. In the case of a roller bearing, the outer surface of the bearing may be an outer surface of an outer race of the bearing. In the case of a roller bearing a surface of an inner race of the bearing may be attached on the crankpin. One sliding shoe may be attached to and associated with one piston.

In a development of the previous embodiment, each sliding shoe is rotatably attached to the bottom end of the associated piston.

Each piston having a separate rotating sliding shoe may provide a high freedom of choice of design as the engagement of each sliding shoe with the crankpin, and thereby the movement of each piston, may be tailored for each piston. The sliding shoes may be rotatably attached to the bottom ends of associated pistons via a bearing such as a plain bearing, roller bearing, or any other suitable bearing. The sliding shoes and/or the pistons may comprise at least one bearing and/or bearing surface for supporting the connecting shaft and allowing a relative rotating motion of the associated sliding shoe and piston. The bearing surface may be a plain bearing surface. The bearing may be a plain bearing (also known as a sliding bearing), roller bearing, or the like. Each piston may comprise a plain bearing or roller bearing in the bottom end of the piston for supporting the associated connecting shaft. Each sliding shoe may comprise at least one plain bearing and/or roller bearing through which the associated connecting shaft extends. The at least one portion of the sliding shoe through which the associated connecting shaft extends may comprise of and/or consist of and/or be coated with a plain bearing material such as metals, metal alloys, or polymers e.g. brass, steel, aluminium or aluminium alloys, bronze, PTFE, and/or combinations thereof such that the sliding shoe itself may constitute a plain bearing for supporting the associated connecting shaft. The connecting shaft may extend through two such portions of the associated sliding shoe. The connecting shaft may extend in the axial direction. The connecting shaft may be secured to the associated piston and sliding shoe through one or more circlips, pins, bolts, or the like. The circlips, pins, bolts, or the like may be positioned at in the axial direction opposite ends of the connecting shaft.

In an embodiment, a housing of the multi-stage compressor comprises at least one guide groove, the at least one guide groove being configured for guiding the movement of at least one guide element attached to a piston.

This may provide freedom of choice of design of compression chamber and associated piston diameters as the walls of the compression chambers need not be configured to guide the pistons. The compressor may comprise at least one guide groove per piston for guiding the movement of at least one guide element attached to the associated piston and/or sliding shoe. The guide groove may be offset in the axial direction from the pistons. The at least one guide groove may extend in the radial direction. The at least one guide groove may extend a length equal to a length of a stroke length of an associated piston. The at least one guide element may be attached to a connecting shaft. The housing of the compressor may comprise at least two guide grooves per piston, the at least two grooves being offset in the axial direction either side of the piston and/or sliding shoe. Each piston and/or sliding shoe may comprise one or more guide elements for being guided in a guide groove. Each guide element may be guided in a separate guide groove. Two guide elements may be attached to a piston and/or sliding shoe, wherein the two guide elements are offset in the axial direction either side of the piston and/or sliding shoe. Two guide elements may be attached to in the axial direction opposite ends of a connecting shaft. Thereby the movement of each piston may be guided. The guide elements may comprise and/or consist of metal or a plain bearing material such as described herein. The guide elements may be secured to the connecting shaft via clips such as circlips. The pistons may be guided such that the one or more pistons do not touch an inner wall of the associated compression chamber and/or such that the one or more pistons only move in the radial direction. This may have the advantages as explained above.

The at least one guide groove and/or the at least one guide element attached to a piston may be configured such that, in operation, the associated piston does not touch an inner wall of the associated compression chamber and/or such that, in operation, the piston only or substantially only move(s) in the radial direction of the compressor.

In an embodiment, the multi-stage compressor comprises one or more linear bearing(s) configured for guiding the movement of an associated piston of the pistons of the multi-stage compressor and/or at least one guide element attached to the associated piston.

The linear bearing may be a slide bushing, a plain bearing, a ball bearing, or the like. The multi-stage compressor may comprise 1, 2, 3, 4, 5, 6, or more linear bearings per piston for guiding the movement of an associated piston and/or at least one guide element attached to the associated piston. Each linear bearing may guide one guide element attached to the associated piston. Additionally or alternatively, the guide element attached to the associated piston may comprise one or more linear bearings. Each linear bearing may slide on a journal and/or a shaft attached in or to the compressor housing. The journal and/or shaft may extend parallel to the associated piston and/or the movement direction of the associated piston. The at least one guide element may comprise two linear bearings each sliding on a journal and/or shaft attached in and/or to the multi-stage compressor housing.

Additionally or alternatively, the multi-stage compressor may comprise 1,2, 3, 4, 5, 6, or more bushing guide bars per piston configured for guiding the movement of an associated piston. The bushing guide bar(s) may be positioned and/or attached in the compressor housing and/or cylinder housing and/or compression chamber, potentially to form an innermost surface of the compression chamber. The innermost surface of the compression chamber may face the associated piston and potentially provide a surface for a piston to slide against. The bushing guide bar(s) may be made of a bushing material. The bushing guide bar(s) may extend parallel to the associated piston and/or the movement direction of the associated piston. The bushing guide bar(s) may alternatively be denoted bushing guide rod(s). The bushing guide bar(s) may extend in the axial direction of the associated piston and may be positioned around the circumference of the associated piston.

Additionally or alternatively, the multi-stage compressor may comprise 1,2, 3, 4, 5, 6, or more guide rollers configured for guiding the movement of an associated piston. The guide rollers may be positioned and/or attached and/or installed and/or mounted in the multi-stage compressor housing and/or cylinder housing. A guide roller may rollingly guide the movement of the associated piston. The guide roller(s) may be positioned along the axial direction of the associated piston and may be positioned around the circumference of the associated piston.

In an embodiment, the compression chamber of at least a first cylinder of the two or more cylinders is connected to the compression chamber of a second cylinder through at least one non-return valve for preventing flow of fluid from the compression chamber of the second cylinder to the compression chamber of the first cylinder.

In this way, fluid may flow from the compression chamber of a given cylinder to the compression chamber of a directly following cylinder i.e. from a first compression stage to the next compression stage of the multi-stage compressor and at flow from a given compression chamber to a compression chamber of a cylinder of a preceding compression stage may be prevented. This may reduce complexity of construction of the compressor as just a single flow channel with a non-return valve between compression chambers of two cylinders may be needed. A compression chamber of a cylinder may be connected to a compression chamber of a directly following and/or directly preceding cylinder through at least one non-return valve. The compression chambers of the cylinders may be connected by non-return valves preventing flow of fluid from a compression chamber of a given cylinder to a compression chamber of a directly preceding cylinder. The at least one non-return valve may prevent fluid from flowing from a given cylinder to a directly preceding cylinder. A non-return valve may be provided between each compression chamber and the compression chamber of the directly following cylinder and/or directly preceding cylinder. The at least one non-return valve may also be denoted a check valve. The at least one non-return valve may be spring loaded. The at least one non-return valve may be a ball check valve, diaphragm check valve, swing check valve, or any other suitable valve. The compression chamber of a final cylinder i.e. the final stage of compression may be connected to the outlet of the compressor. The compression chamber of a final cylinder may be connected to the outlet of the compressor through at least one non-return valve. The inlet of the compressor may be connected to the compression chamber of a first cylinder i.e. the first compression stage of the compressor through at least one non-return valve. In this way a compressed fluid may pass from the inlet and successively through the compression chambers of the successive cylinders to, and out of, the outlet, and flow of fluid from the outlet through preceding compression chambers of preceding cylinders may be prevented. The non-return valve may be located externally of the two or more cylinders. The non-return valve may be located in a valve housing that is attachable to and detachable from a cylinder and/or cylinder housing and/or compressor and/or compressor housing.

In an embodiment, the at least one non-return valve is located externally of the two or more cylinders inside a valve pipe such that a fluid flowing from the compression chamber of at least a first cylinder to the compression chamber of a second cylinder flows through the valve pipe and the at least one non-return valve.

The term “located externally of the two or more cylinders” throughout this disclosure may be understood as not being located in or within a cylinder and/or cylinder housing of the two or more cylinders.

In this way there may be a high freedom of choice of design of the compressor, particularly the cylinders and cylinder housings as the connection of the compression chambers as well as the non-return valves may be provided separately and/or externally of the cylinders or a housing thereof. A valve pipe may constitute a part of a compression chamber. A compression chamber may comprise at least a part of a valve pipe. The valve pipe may comprise a pipe volume for the fluid to flow through either side of the non-return valve. The compression chamber may comprise a pipe volume of a valve pipe. The compression chamber may be directly connected to a pipe volume. The valve pipe may be a cylindrical pipe. The, or a, valve pipe may extend between a given cylinder and a directly following cylinder or a preceding cylinder. A valve pipe may be provided between each compression chamber and the compression chamber of a directly following cylinder and/or directly preceding cylinder. A or one or more, potentially all valve pipe(s) may be positioned within an outer circumferential periphery of the compressor and/or cylinder(s) and/or cylinder housing(s). A or one or more, potentially all valve pipe(s) may be positioned closer to a center and/or the rotation axis of the compressor than an outermost part of a or the cylinder(s) and/or cylinder housing(s). Said outermost part of the cylinder(s) and/or cylinder housing(s) potentially being a part of the cylinder(s) and/or cylinder housing(s) positioned farthest away from the center and/or the rotation axis of the compressor. The at least one non-return valve may be positioned inside the valve pipe halfway along a length the valve pipe extends between a given cylinder and a directly following cylinder. The valve pipe may comprise an inlet end and an outlet end. The valve pipe may have a valve pipe length extending between the inlet end of the valve pipe and the outlet end of the valve pipe. One or more, potentially all, valve pipe(s) may be substantially straight or straight. The term “straight” may be understood as the pipe extending substantially only or only in one direction. One or more, or all, valve pipe(s) may substantially extend or extend between an outer side wall of a given cylinder and/or cylinder housing and an outer side wall of directly following or preceding cylinder and or cylinder housing. A valve pipe may extend substantially straight and/or straight between said respective outer side walls. A, or one or more, or each, or all valve pipe(s) may extend substantially straight and/or straight between outer side walls of directly following and/or directly preceding cylinders and/or cylinder housing(s). The at least one non-return valve may prevent flow of fluid in a direction from the outlet end to the inlet end of the valve pipe. A first pipe volume may be a pipe volume extending from an inlet end of the valve pipe to the non-return valve. A second pipe volume may be a pipe volume extending from the non-return valve to the outlet end of the valve pipe. At least one compression chamber may comprise a first pipe volume. The non-return valve may be positioned nearer the inlet end of the valve pipe than the outlet end of the valve pipe. The non-return valve may be positioned less than 1/100, 1/75, 1/50, 1/40, 1/30, 1/25, 1/20, 1/15, 1/10, 1/9, ⅛, 1/7, ⅙, ⅕, ¼, ⅓ of a valve pipe length from the inlet end of the valve pipe. The at least one non-return valve may be positioned inside the valve pipe equidistantly from the inlet end and the outlet end. The valve pipe may comprise a sealing element at its inlet end and/or outlet end for sealing against a housing of a cylinder. The inlet end and/or outlet end of the valve pipe may be rounded and/or spherical. The cylinder housing may comprise openings corresponding to the shape of the inlet end and/or outlet end of the valve pipe to receive the inlet end and/or outlet end. In this way the valve pipe may be conveniently attached to or removed from a housing of a cylinder of the compressor. The valve pipe may comprise a first and a second valve pipe part. The first and second valve pipe parts may be detachable from each other such that the valve pipe may be disassembled into a disassembled state where the first and second valve pipe parts are disconnected. The first and second valve parts may be attachable to each other into an assembled state where the first and second valve pipe parts are connected. The first and second valve pipe parts may be attached to each other via a thread. The first valve pipe part may comprise a thread matching a thread on the second valve pipe part for assembly and disassembly of the first and second valve pipe parts. The first and second valve pipe parts may each constitute one half of the valve pipe. A sealing element may be disposed between the first and second valve pipe parts in the assembled state. The valve pipes may be cooled by a cooling device. A cooling device such as a cooling jacket for cooling the valve pipe may attached to the valve pipe. The cooling device may be disposed around the valve pipe. The cooling jacket may be connected to one or more cooling pipes. The cooling pipes may be connected to one or more cooling channels. The cooling jacket may be connected to one or more cooling channels. In this way the cooling jacket may be part of the cooling circuit of the compressor and both the two or more cylinders and the valve pipes may be cooled. The cooling jacket and connected valve pipes and/or connected cooling channels may form a cooling circuit that is separate of the cooling circuit for cooling the cylinders. In the disassembled state of the valve pipe the at least one non-return valve may be exposed. The at least one non-return valve may be seated in the first and/or second valve pipe part. The at least one non-return valve may be detachably attached to the first and/or second valve pipe part. The at least one non-return valve may be threaded into the first or second valve pipe part. A non-return valve may be positioned at an inlet end of the valve pipe(s) and an outlet end of the valve pipe(s). The volume between the non-return valves at the inlet end and the outlet end of the valve pipe(s) may be considered a pipe volume. This may provide a buffer for compressed fluid between compression chambers.

The one or more cooling pipes may extend between the cylinders in parallel with the valve pipes.

In a development of the previous embodiment, the valve pipe(s) is/are removably attached between two cylinders.

This may provide a compressor that is easy to maintain and/or adapt to different use cases, as the valve pipes may be quickly and easily replaced or swapped for a different version e.g. with a higher rated non-return valve for higher pressure applications.

The valve pipe(s) may be removably attached to a cylinder by press fit, clip in, snap lock and/or threading. The valve pipe(s) may be removably attached such that the valve pipe(s) may be removed by hand i.e. without use of a tool. An inlet end and/or outlet end of a valve pipe may be removably attached in a cylinder.

In an embodiment, at least one compression chamber comprises a first pipe volume of a valve pipe.

In an embodiment, the valve pipe(s) extend between a given cylinder and a directly following cylinder.

In an embodiment, the valve pipe(s) is/are provided between each compression chamber and the compression chamber of a directly following cylinder and/or directly preceding cylinder.

In an embodiment, one or more, potentially all, valve pipe(s) is/are substantially straight.

In an embodiment, one or more, potentially all valve pipe(s) is/are positioned within an outer circumferential periphery of the compressor and/or cylinder(s) and/or cylinder housing(s).

In an embodiment, one or more, potentially all valve pipe(s) are positioned closer to a center and/or a rotation axis about which the crankpin rotates than an outermost part of a or the cylinder(s) and/or cylinder housing(s).

In an embodiment, one or more of the valve pipe(s) extend(s) substantially straight and/or straight between outer side walls of directly following and/or directly preceding cylinders and/or cylinder housing(s).

In an embodiment, one or more of the pistons are of different diameters.

In this way the compressor may be tailored to specific use cases as piston and/or cylinder diameters may be chosen for the compressor to deliver the required pressure output from a given pressure input.

In an embodiment, for at least one cylinder a cylinder housing comprising the associated compression chamber of the given cylinder is detachable from and attachable to the compressor.

In this way the compressor may be simple to maintain and/or adapt to a specific use case as cylinder housings may be quickly swapped or replaced with a different cylinder housing with e.g. a different diameter compression chamber in order for compressor to deliver a desired pressure output.

The cylinder housing may be detachable from and attachable to a cylinder base. The cylinder base may include a linear seal such as a piston seal and/or rod seal for sealing between the associated piston and cylinder. At least one, two, three, four, five, six, or more cylinder bases may include a linear seal such as a rod seal for sealing between the associated piston and cylinder. The rod seal may have a height extending in the radial direction of the compressor equal to or less than ½, 9/20, ⅖, 7/20, 3/10, ¼, ⅕, 3/20, 1/10, 1/20 of the stroke length of the associated piston. The height of the rod seal may extend in parallel to the length of the associated piston. A rod seal may alternatively be denoted shaft seal. One or more, potentially all, cylinder base(s) may be attached, potentially detachably attached to the compressor housing.

At standstill and/or in operation of the compressor, one or more of the pistons may substantially only or only contact the associated linear seal such as a rod seal. The associated linear seal may be included in the associated cylinder base and/or comprised by the associated cylinder. At standstill and/or in operation of the compressor, two or more of the pistons may substantially only contact or only contact the associated linear seal included in the cylinder base and/or comprised by the cylinder. At standstill and/or in operation of the compressor, all pistons may substantially only contact or only contact the associated linear seal such as a rod seal. Said associated linear seal potentially being included in the cylinder base and/or comprised by the cylinder.

Experiments have shown that a rod and/or shaft seal located in the cylinder housing perform better at higher pressures than seals located on the piston. This may be due to the larger amount of space available for rod and/or shaft sealings located in the cylinder housing in both the radial and axial direction of the piston compared to seals such as piston rings located on the piston. This may provide a greater choice of size, material, and/or shape of the seal. This may facilitate reduced friction and/or an improved seal during operation of the compressor.

In an embodiment, the compression chambers of one or more of the cylinders are of different diameters.

In this way the compressor may be tailored and/or configured for a particular use case as compression chamber diameters may be chosen for the compressor to deliver the required pressure output from a given pressure input.

Each compression chamber of the two more cylinders may be of a different diameter. The pistons may be of a diameter corresponding to the diameter of the respective compression chamber.

In an embodiment, each sliding shoe is secured to the crankpin by an associated separate annular holding ring which encloses a circumference of the crankpin.

In this way engagement of the sliding shoes and crankpin may be secured as the sliding shoe may be held to the crankpin. Furthermore, it may improve the freedom of choice of design of the compressor including cylinders, compressions chambers, pistons, sliding shoes etc. as holding rings may be individually configured and designed.

The term “separate” may be understood as not forming part of other components i.e. being a distinct part in itself.

Additionally or alternatively, the holding rings may enclose a circumference of a holding ring bearing mounted on the crankpin. The holding rings may grip the circumference of the crankpin and/or circumference of a holding ring bearing mounted on the crankpin. The holding rings may directly contact the circumference of the crankpin. The holding rings may be located on a holding ring bearing mounted on the crankpin. The holding ring bearing may be a plain bearing or a roller bearing such as described herein. The holding rings may be secured to the crankpin between two bearings mounted on the crankpin. Each, or one or more, sliding shoe(s) may comprise a recess or opening for receiving a holding ring. The recess or opening for receiving the holding ring may be located in and/or extend through the sliding surface. The holding rings may be attached in an opening of the associated sliding shoe. The holding rings may extend through an opening of the associated sliding shoe. The holding rings may be detachable from the associated sliding shoe. The holding rings may be attached to the associated sliding shoe via one or more bolts, screws, clips, pins, and/or clasps. The holding rings may be rigidly attached to the sliding shoes i.e. such that relative movement of the associated holding ring and sliding shoe is prevented. The holding rings may comprise, consist of, and/or be coated with the same material as the crankpin and/or sliding shoes. Each sliding shoe may comprise a threaded hole for receiving a bolt or screw for securing an associated holding ring to the sliding shoe. Each holding ring may comprise a through hole for receiving a bolt or screw. Each holding ring may comprise a threaded through hole for receiving a bolt or screw. The holding rings may comprise, consist of, and/or be coated with a plain bearing material such as e.g. metals, metal alloys, or polymers e.g. brass, steel, aluminium or aluminium alloys, bronze, PTFE, and/or combinations thereof. Additionally or alternatively, the holding ring bearing may be two or more holding ring bearings. The holding ring bearing(s) may be separate from the one or more crankpin bearings. The holding ring bearing(s) may be located between two bearings mounted on the crankpin i.e. crankpin bearings. The holding ring bearing(s) may have a smaller outer diameter than the one or more crankpin bearings. The holding rings may abut each other. In this way the compressor may be made more compact. By making the holding rings out of a bearing material the frictional force between them may be reduced, thereby improving the efficiency of the compressor. Furthermore, the holding rings abutting each other may ensure that the holding rings do not move axially on the holding ring bearing(s) and/or crankpin and may further improve stability of the movement of the pistons. The holding rings may be positioned between two crankpin bearings two abut the two bearings. In other words, the holding rings may be sandwiched between two crank bearings. This may help to further ensure that the holding rings to do not move axially on the crankpin and/or holding ring bearing(s) and further improve the stability of the movement of the pistons. Using axial-radial bearings as the crankpin bearings may reduce the friction against movement of the holding rings sandwiched between the crankpin bearings.

In a development of the previous embodiment, the holding rings are located on a bearing mounted on the crankpin.

In this way energy lost to friction between moving parts may be reduced as the bearing may lower the friction between the holding rings and the crankpin.

In an embodiment, the holding ring(s) enclose a circumference of a holding ring bearing mounted on the crankpin.

In an embodiment, the holding rings grip the circumference of the holding ring bearing.

In an embodiment, the holding rings are secured to the crankpin between two bearings mounted on the crankpin.

In an embodiment, one or more sliding shoe(s) comprise(s) a recess or opening for receiving a holding ring.

In development of the previous embodiment, the recess or opening for receiving the holding ring is located in and/or extends through a sliding surface of the one or more sliding shoe(s) for engaging with the crankpin and/or a crankpin bearing.

In an embodiment, the compressor is configured such that, in operation and/or at standstill, at least one or each piston do(es) substantially not touch an inner wall of the associated compression chamber.

In an embodiment, the compressor is configured such that, in operation, at least one or each piston only or substantially only move(s) in the radial direction of the compressor.

In an embodiment, the at least one guide groove and/or the at least one guide element attached to a piston is/are configured such that, in operation, the associated piston does not touch an inner wall of the associated compression chamber and/or such that, in operation, the piston only or substantially only move(s) in the radial direction of the compressor.

In an embodiment, the first cylinder comprises one or more associated rod seals for sealing against an associated piston of the first cylinder.

In an embodiment, a cylinder base of the first cylinder comprises an associated rod seal for sealing between the first cylinder and its associated piston.

In an embodiment, the rod seal has a height extending in the radial direction of the compressor, said height being equal to or less than ½ of a stroke length of the associated piston.

In an embodiment, at standstill and/or in operation of the compressor, the associated piston of the first cylinder substantially only contacts the associated rod seal of the first cylinder.

In an embodiment, the pistons do not comprise any seal, such as for example a piston ring or a piston seal, potentially attached to and/or mounted on the piston.

In an embodiment, the crankpin and/or a crankpin bearing(s) provided on the crankpin has/have an outer diameter that is at least 1.1 times a smallest and/or largest stroke length of each of the pistons.

In an embodiment, a length of a lever arm acting on a rotation axis about which the crankpin rotates is equal to or less than 200% of a smallest and/or largest stroke length of each of the pistons.

In an embodiment the compressor comprises a rotatable crankshaft comprising at least two interconnected separate shafts extending in parallel with the crankpin, wherein the crankpin interconnects the two of the at least two interconnected shafts by being clamped to a respective end of each of the two shafts by a detachable clamp mechanism.

In this way the compressor may be easy to disassemble as the crankpin and crankshaft may be disassembled from each other. This may improve serviceability. Further still, it may allow the compressor to be adapted to different use cases, by interchanging parts.

In an additional or alternative embodiment, at least one sliding shoe is rotatably attached to an associated piston via a connecting shaft extending through the sliding shoe and the associated piston, wherein at least one guide element configured for being guided in the at least one guide groove is attached to the connecting shaft.

In this way the drive and movement of the piston may be guided and secured by the at least one guide element in the at least one guide groove.

The compressor may have a largest dimension equal to or less than 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3. 0.2, or 0.1 meter. The largest dimension may be a largest dimension of the compressor extending in the radial direction of the compressor or the axial direction of the compressor.

A second aspect of the disclosure concerns a method for compressing a fluid in a multi-stage compressor, the compressor comprising:

-   -   two or more cylinders, each cylinder having a compression         chamber and a piston, so that a fluid in each of the compression         chambers is compressed by the associated piston;     -   the cylinders being connected in series such that a fluid         entering an inlet of the compressor is compressed to a first         pressure in the compression chamber of a first cylinder and,         then, enters into the compression chamber of a second cylinder         where the compressed fluid is compressed to a second higher         pressure; and     -   wherein each piston is driven by one and the same crankpin of         the compressor.

If more than two cylinders are present, the fluid successively enters into and is compressed to a successively higher pressure in the compression chamber(s) of the additional cylinder(s), before the fluid exits from an outlet of the compressor.

In an embodiment, the multi-stage compressor further comprises at least one supply compressor supplying compressed fluid at a pressure above atmospheric pressure to the compression chamber of the first cylinder, wherein the supply compressor and the pistons is driven by one and the same crankshaft, potentially the one and same crankpin, as the pistons of the multi-stage compressor.

In a third aspect, the disclosure concerns a system for compressing a fluid, the system comprising:

-   -   a multi-stage compressor according to the first aspect of the         disclosure and     -   a second compressor configured to provide fluid at a pressure         above atmospheric pressure to the inlet of the multi-stage         compressor and/or the compression chamber of the first cylinder.

In an embodiment, the second compressor is a stationary or fixed compressor.

A stationary or fixed compressor may be understood as a compressor that is installed and/or mounted and/or fixed to a location, and which has to be uninstalled and/or unmounted to be moved from said location. The second compressor may be a compressor supplying a compressed air system and/or air line and/or air piping system such as may be used in a workshop, factory, and/or industrial plant.

In an embodiment, the second compressor is comprised by and/or part of the multi-stage compressor.

In an embodiment the system further comprises one or more components selected from the following list: a gas filter and/or a fluid filter and/or a cooling device and/or a cooling fluid tank and/or a power supply and/or a power generator, and/or a drive unit for driving the multi-stage compressor, and/or a compressed fluid tank, wherein, in the given case, the multi-stage compressor is connected the fluid tank for supplying compressed fluid to the compressed fluid tank.

The compressed fluid tank may be a compressed liquid tank or a compressed gas tank, such as an air tank. The gas filter may be carbon filtering device (clean air)

The cooling device may be a cryogenic cooling device also known as a cryocooler. The power generator may be for supplying power to a given application such as the drive unit for driving the multi-stage compressor and/or other external applications. The power generator may be driven by a sustainable energy source such as solar, wind, hydro, and/or surplus energy, or the like. This may contribute to sustainability and reduction of CO2 emissions (CO2 neutrality), especially when the power generator is driven by energy from sources in the above. The system may optionally furthermore comprise a container in which one or more of the components of the system are placed. In an embodiment the power generator is a compressed air driven power generator. The power generator may be driven by compressed air from the compressed air tank supplied by the multi-stage compressor and/or directly from the multi-stage compressor.

In an embodiment, the multi-stage compressor is a portable compressor. In an embodiment, the second compressor is a multi-stage compressor according to according to the first aspect of the disclosure.

In an embodiment, the second compressor is a supply compressor for supplying compressed fluid at a pressure above atmospheric pressure to the compression chamber of the first cylinder, wherein the supply compressor and the pistons is driven by one and the same crankshaft, potentially the one and same crankpin, as the pistons of the multi-stage compressor.

In an embodiment, the multi-stage compressor and the second compressor are powered by the same drive unit.

The crankshafts of the multi-stage compressor and the second compressor may be coupled together to transmit drive between the compressors. Two, three, four, five or more compressors may be powered by the same drive unit. The crankshafts of the two, three, four, five or more compressors may be coupled together. Additionally or alternatively, the multi-stage and second, third, fourth, fifth or more compressors may share a common crankshaft. Two, three, four, five or more compressors according to the present disclosure may be connected in series or parallel. An additional compressor, potentially a multi-stage compressor according to the first aspect of this disclosure, may be connected to each of compressors connected in parallel or to a first of the compressors connected in series. The single additional compressor may provide a fluid at a pressure above atmospheric pressure to the inlet of the associated compressor(s).

In a fourth aspect, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for energy storage.

In an embodiment, the energy storage is compressed-fluid energy storage

The fluid may be air, water, fossil fuels such as fossil fuel gasses and/or liquids. The compressor may be used for filling compressed air tanks with compressed air for use in pumping tires, powering air rifles, filling gas tanks e.g. oxygen or other gas tanks, powering generators for production of electricity, powering machinery, powering air motors in applications such as vehicles, workshops, factories, industrial plants and the like. Additionally or alternatively, the compressor may be used for providing compressed liquid e.g. water for industrial applications such as cutting of different materials with the compressed liquid, powering generators for production of electricity, driving machinery.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for energy storage for storing compressed fluid for driving a power generator.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for energy storage compressed gas, potentially compressed air, storage.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for compressing a fluid.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure, wherein the multi-stage compressor is connected to a second compressor.

In an embodiment the second compressor provides fluid at a pressure above atmospheric pressure to the inlet of the multi-stage compressor.

In an embodiment the second compressor is a stationary or fixed compressor installation.

In a development of the previous embodiment, the stationary or fixed compressor installation is installed in a gas station, workshop, garage, or building.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for charging an air-driven gun, rifle, bow or the like.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for charging a hydraulic or pneumatic damper, spring, suspension system or the like.

In an embodiment, the disclosure concerns use of a multi-stage compressor according to the first aspect of the disclosure and/or a system according to the third aspect of the disclosure for filling a fluid tank or air tank, tire, an inflatable, inflatable device, or the like.

A person skilled in the art will appreciate that any one or more of the above aspects of this disclosure and embodiments thereof may be combined with any one or more of the other aspects and embodiments thereof.

BRIEF DESCRIPTION OF DRAWINGS

In the following, non-limiting exemplary embodiments will be described in greater detail with reference to the drawings, in which:

FIG. 1 shows a perspective view of the front side of the assembled multi-stage compressor,

FIG. 2 shows a perspective view of the rear side of the compressor in FIG. 1 ,

FIG. 3 shows a side view of the compressor in FIG. 2 ,

FIG. 4 shows a section view along line A-A of the compressor in FIG. 3 ,

FIG. 5 shows a partially exploded view of the compressor in FIG. 1 ,

FIG. 6 shows an enlarged detail view of the crankpin, piston, and sliding shoe assembly of the compressor in FIG. 5 , and

FIG. 7 shows an exploded view of the crankpin and piston assembly seen in FIG. 6 ,

FIG. 8 shows the multi-stage compressor with an alternative embodiment of the cooling pipes and cooling jacket,

FIG. 9 shows an embodiment of the multi-stage compressor comprising supply compressors,

FIG. 10 shows a cross-section through the multi-stage compressor in FIG. 10 corresponding to the cross-section shown in FIG. 4 ,

FIG. 11 shows a close up of the cross-section of a supply compressor from FIG. 10 ,

FIG. 12 shows an alternative piston movement guide,

FIG. 13 shows a second alternative piston movement guide, and

FIG. 14 shows a third alternative piston movement guide.

DETAILED DESCRIPTION OF DRAWINGS

Starting with FIG. 1 a multi-stage compressor 1 according to the present disclosure is seen from the front. The compressor 1 comprises three cylinders 2 a, 2 b, 2 c each with a cylinder housing 22. The cylinders are interconnected by valve pipes 7 which in this embodiment have cooling jackets 71 for cooling the valve pipes 7 attached to them. Extending in parallel to the valve pipes 7 are cooling pipes 26 for cooling the cylinders 2 a, 2 b, 2 c. The cooling pipes 26 connect cooling channels (not shown) in the cylinder housings 22 to allow a flow of cooling medium for cooling the cylinders 2 a, 2 b, 2 c to flow through the compressor 1. The compressor 1 further comprises an inlet 12 for fluid to enter a first cylinder of the compressor 1 and an outlet 13 for exiting a final cylinder of the compressor 1. The fluid supplied to the inlet 12 of the compressor 1 may be pressurized or pre-compressed such that the fluid being compressed in the first cylinder 2 a is already pressurized before being compressed in the cylinder. For example the fluid supplied to the inlet may be pressurized to 8 bar as in the present example. The compressor further has a crankshaft 6 which comprises two interconnected separate shafts 61. One of the shafts 61 is configured for being connected to a drive unit for driving the compressor 61 i.e. rotating the crankpin 5 and the other shaft 61 exiting the rear side of the compressor is optionally configured for being connected to and drive a second compressor.

Moving to FIG. 2 where the compressor 1 is seen from the rear side, the guide elements 33 for guiding the movement of pistons 3 are seen guided in guide grooves 15. As can be seen in FIGS. 1 and 2 , the majority of components of the compressor 1 are connected to each other via bolts 16 e.g. the compressor housing 11, cylinder housings 22, inlet 12, outlet 13, and shield plate 17. This allows easy assembly/disassembly as well as maintenance and swapping of components to suit different use cases. In FIG. 3 the compressor 1 is seen from a side, where it can be seen that the two interconnected shafts 61 of the crankshaft 6 are concentric and extend an equal length from the compressor housing 11.

Moving to FIG. 4 a section view of the compressor 1 along line A-A in FIG. 3 , where the sliding shoes have been removed, is shown. Here the compression chambers 21 in the cylinders 2 a, 2 b, 2 c and the associated cylindrical pistons 3 can be seen. The cylinders 2 a, 2 b, 2 c are located about the rotation axis RA and extend in a radial direction away from rotation axis RA. The compression chambers 21 which are located within the cylinders are of different diameters with the associated pistons 3 having a corresponding diameter d i.e. the pistons 3 are of diameters corresponding to the diameter of the associated compression chambers 21. In this way the compressor 1 is tailored to deliver a fluid at a certain output pressure at the outlet 13 of FIG. 1 from a fluid entering the inlet 12 of FIG. 1 at a given input pressure.

When the crankshaft 6 is driven and thereby rotated, the crankpin 5 is rotated about the rotation axis RA whereby the pistons 3 are driven in and out of the associated compression chamber 21 to compress a fluid therein. As is more clearly seen in FIG. 6 , the driving in and out of the pistons 3 is achieved by the sliding shoes 4 engaging with crankpin bearings 51 mounted on the crankpin 5 and the holding rings 42 enclosing a circumference of a holding ring bearing 44 on the crankpin 5. As the crankpin 5 then rotates about the rotational axis RA, dependent on its relative position to the pistons, it either pushes the pistons 3 into the associated compression chamber by means of the sliding shoes 4, which engage with the crankpin bearings 51 and which are connected to the pistons 3 via connecting shafts 43, or pulls the pistons 3 out of the associated compression chambers 21 by means of the separate holding rings 42, which are attached to an associated sliding shoe 4 and secured to the crankpin 5 by enclosing a circumference of the crankpin 5 and the holding ring bearing 44 mounted on the crankpin 5. It can also be seen how the compression chambers 21 of the cylinders 2 a, 2 b, 2 c are connected through non-return valves 72 to the compression chamber of the directly following cylinder. The respective chambers are connected through one non-return valve 72 for preventing flow of fluid from the compression chamber 21 of the given cylinder 2 a, 2 b, 2 c to the compression chamber of the directly preceding cylinder. In the shown embodiment, the non-return valves 72 are located in cylindrical valve pipes 7 which comprise a pipe volume for fluid to flow through either side of the non-return valve 72. Thereby, in the embodiment shown, a fluid may enter the compression chamber 21 of the first cylinder 2 a where it is compressed by the associated piston 3, and, then flows through the flow channel 28 and through the non-return valve 72 in the valve pipe 7 and into the compression chamber 21 of the second cylinder 2 b where the fluid is further compressed by the associated piston 3 and flows through the next flow channel 28 and through the non-return valve 72 in the valve pipe 7 into the compression chamber 21 of the third cylinder 2 c, where the fluid is even further compressed by the associated piston 3 and flows through the outlet 13 of the compressor 1. The spherical inlet ends 73 and outlet ends 74 of the valve pipes each comprise a sealing element and are press fit into the cylinder housings 22 of the cylinders 2 a, 2 b, 2 c.

The compressor and its components are configured such that in operation, the pistons 3 move substantially only in the radial direction of the compressor 1 and in an axial direction of the respective piston 3 in the compression chambers 21.

In FIG. 4 , it can also be seen that the separate annular holding rings 42 enclose a circumference of a holding ring bearing 44 mounted on the crankpin 5. The holding rings 42 are attached to the associated sliding shoes 4 via a bolt 16 that extends through the sliding shoe 4 (best seen in FIG. 7 ) and into the bolt hole 45 of the associated holding ring 42. For demonstration purposes, the rotation axis RA is shown in FIG. 4 and FIG. 6 , whereby it can be seen that the crankpin 5 is positioned with a distance of 0.3 crankpin radii from the periphery of the crankpin 5 to the rotation axis RA. Furthermore, it can be seen that cylinders 2 a, 2 b, 2 c comprise rod seals 24 for sealing against their associated piston. At standstill and in operation of the compressor, the associated piston 3 each cylinder 2 a, 2 b, 2 c substantially only contacts the associated rod seal 24 of each cylinder. The pistons 3 also do not comprise any seal, such as for example a piston ring or a piston seal attached to and/or mounted on the piston 3.

Turning to FIG. 5 which shows a partially exploded view of the compressor 1, the manner in which the compressor 1 may be assembled and disassembled, and how components may be swapped out or replaced becomes apparent. The valve pipes 7 comprise a first and second valve pipe part 7 a, 7 b which can be disassembled from each other as shown. The valve pipe parts 7 a,7 b are attached to each other via a thread, where the non-return valve 72 is seated and threaded into the first valve pipe part 7 a. The crankshaft bearings 62 for supporting the crankshaft 6 in the compressor housing 11 are seen positioned on shaft 61 of the crankshaft 6. As can also be seen, the cylinder housings 22 comprising the associated compression chamber 21 of the given cylinder 2 a, 2 b, 2 c is detachable from and attachable to the compressor 1, more specifically from a cylinder base 27.

FIG. 6 shows an enlarged detail view of the crankpin, piston, and sliding shoe assembly. Each sliding shoe 4 is rotatably attached to an associated piston 3 via a connecting shaft 43 extending through the bottom end of the associated piston 3 and two portions of the associated sliding shoe 4. Each piston 3 comprises a plain bearing 46 positioned in the bottom end of the piston 3 for supporting the associated connecting shaft. Each piston 3 has a length “L” extending in the radial direction from a top surface of a top end to a bottom surface of a bottom end of the piston. The sliding shoes 4 are made of bronze, whereby the sliding shoe 4 itself may constitute a plain bearing for supporting the associated connecting shaft 46. The connecting shafts 43 extend in the axial direction and are secured to the associated piston 3 and sliding shoe 4 through two circlips 45 positioned at in the axial direction opposite ends of the connecting shaft 43. Two guide elements 33 are also attached to in the axial direction opposite ends of the connecting shaft 43 and secured to the connecting shaft by the circlips 45. A distance D from the center axis CA (FIG. 6 ) of the crankpin 5 to the rotational axis RA is about 1 crankpin radii. Two crankpin bearings 51 for engaging with the sliding shoes 4 are mounted on the crankpin 5.

As is best seen in FIG. 7 , the sliding shoes 4 comprise a sliding surface 41 which is shaped form-fittingly to the crankpin bearings 51 for engaging with the crankpin bearings 51. The sliding surface 41 further has an opening 47 for receiving the holding rings 42 which are secured therein by a bolt 16 extending through the associated sliding shoe 4 and into bolt hole 48.

FIG. 8 shows an alternative embodiment of the cooling pipes 26 and cooling jacket 71. In this embodiment some of the cooling pipes 26 which are connected to the cooling channels (not shown) in the cylinders 2 a, 2 b, 2 c connect to the cooling jackets 71 and enter into the cooling jacket 71 such that the valve pipes 7 and the fluid therein can be cooled. In this way the cooling jackets 71 form a part of the cooling circuit for the cylinders 2 a, 2 b, 2 c, whereby both the valve pipes and the cylinders 2 a, 2 b, 2 c can be cooled.

In the shown embodiment, the compressor housing 11, cylinder housing 22, valve pipes 7, cooling jacket 71, cooling pipes 26, and shield plate 17 are made of aluminium. The cylinder base 27, connecting shafts 43, crankpin 5, crankshaft 6, and clamp mechanism 63 are made of steel, with the pistons 3 being made of steel with an aluminium core. The sliding shoes 4 are made of bronze, with the holding rings 42 and guide elements 45 being made of a combination of bronze and steel.

Turning now to FIGS. 9 and 10 , an embodiment of the multi-stage compressor 1 further comprising three supply compressors 8 for supplying compressed fluid at a pressure above atmospheric pressure to the compression chamber 21 of the first cylinder 2 a via inlet 12 is shown. Identical or similar components have been giving the same references signs as in FIGS. 1 to 8 . The supply compressors 8, positioned within an outer periphery of the multi-stage compressor 1, and the pistons 3 are driven by one and the same crankshaft 6 and crankpin 5. As the crank pin 5 rotates it actuates the supply compressor arm 81 which in turn actuates a spring loaded piston assembly 82 inside the supply compressor 8, whereby fluid is compressed to about 8 bar and out of the outlet 83 and into the inlet of the compressor 1 and the compression chamber 21 of the first cylinder 2 a through respective supply pipes (not shown). The multi-stage compressor 1 then compresses this fluid as described in the above. The supply compressors 8 positioned circumferentially around the crankshaft 6 and crankpin 5 and partly inside the multi-stage compressor housing 2 operate in parallel. Additionally or alternatively, one or more supply compressor 8 may be positioned outside of the multi-stage compressor housing 2 circumferentially around the one and same crankshaft 6, 61 extending externally out of the compressor housing 2. Each of the one or more supply compressors may here potentially be driven by one and the same second crankpin. An enlarged cross-section through a supply compressor 8 is shown in FIG. 11

In the examples shown in FIGS. 1 to 11 , the movement of the pistons 3 is guided by the guide grooves 15 and the guide elements 3 attached to the pistons 4 configured such that, in operation and at standstill, the associated pistons 3 do not touch an inner wall of the associated compression chamber 21 and such that, in operation, the pistons 3 only or substantially only move in the radial direction of the compressor 1. The movement of the pistons 3 may however be guided in other ways such as for example shown in FIGS. 12 to 14 .

FIG. 12 shows a piston 3 and a guide element 33 comprising two linear bearings 9 in the form of slide bushings each sliding along a journal 91 in the form of a shaft. The journal 91 can be attached in or to the multi-stage compressor housing 2.

Additionally or alternatively, the multi-stage compressor 1 may comprise a number of bushing guide bars 92 per piston 3 as seen in FIG. 13 , in this case three, configured for guiding the movement of the associated piston 3. The bushing guide bars 92 can be positioned and attached in the cylinder housing 22 and the compression chamber 21, to form an innermost surface of the compression chamber 21 facing the associated piston 3 and potentially providing a surface for the piston 3 to slide against. The bushing guide bars 92 extend parallel to the associated piston 3 and the movement direction of the piston 3.

Additionally or alternatively, as shown in FIG. 13 the multi-stage compressor 1 may a number of guide rollers 93, six in this shown case, configured for guiding the movement of the associated piston 3. The guide rollers 93 are positioned and attached in the multi-stage compressor housing 2 and the cylinder housing 2 to such that they can rollingly guide the movement of the associated piston 3. The guide rollers 93 are positioned along the axial direction of the associated piston 3 and around the circumference of the associated piston 3.

The multi-stage compressor may further form part of a system comprising a gas filter, a fluid filter, a cooling device such as a cryocooler, a cooling fluid tank, a power supply, a power generator, a drive unit for driving the multi-stage compressor, a compressed fluid tank, wherein, in the given case, the multi-stage compressor is connected the compressed fluid tank for supplying compressed fluid to the compressed fluid tank. The power generator may supply power to a given application such as the drive unit for driving the multi-stage compressor and other external applications. The power generator may be driven by a sustainable energy source such as solar, wind, hydro, and/or surplus energy, or the like. The system may furthermore comprise a container in which one or more of the components of the system are placed. The power generator for example may be a compressed air driven power generator driven by compressed air from the compressed fluid or air tank supplied by the multi-stage compressor and/or may be driven directly from the multi-stage compressor when power for other external applications are needed.

LIST OF REFERENCE NUMERALS

-   1 Multi-stage compressor -   11 Compressor housing -   12 Inlet -   13 Outlet -   14 Cooling pipes -   15 Guide groove -   16 Bolt -   17 Shield plate -   2 a, 2 b, 2 c Cylinder -   21 Compression chamber -   22 Cylinder housing -   24 Rod seal -   25 Cooling channel -   26 Cooling pipe -   27 Cylinder base -   28 Flow channel -   3 Piston -   31 Piston top end -   32 Piston bottom end -   33 Guide element -   4 Sliding shoe -   41 Sliding surface -   42 Holding ring -   43 Connecting shaft -   44 Holding ring bearing -   45 Circlip -   46 Bearing -   47 Opening -   48 Bolt hole -   5 Crankpin -   51 Crankpin bearing -   6 Crankshaft -   61 Separate shaft -   62 Crankshaft bearing -   63 Clamp mechanism -   7 Valve pipe -   7 a First valve pipe part -   7 b Second valve pipe part -   71 Cooling jacket -   72 Non-return valve -   73 Valve pipe inlet end -   74 Valve pipe outlet end -   8 Supply compressor -   81 Actuator arm of supply compressor -   82 Piston assembly of supply compressor -   83 Outlet of supply compressor -   9 Linear bearing -   91 Journal -   92 Bushing guide bar -   93 Guide rollers -   RA Rotation axis -   CA Center axis of crankpin -   D Distance from crankpin to rotation axis -   d Piston diameter -   L Piston length 

1-55. (canceled)
 56. A multi-stage compressor for compressing a fluid, the compressor comprising: two or more cylinders, each cylinder having a compression chamber and a piston, so that a fluid in each of the compression chambers can be compressed by the associated piston; the cylinders being connected in series such that a fluid entering an inlet of the compressor can be compressed to a first pressure in the compression chamber of a first cylinder, and, then enter into the compression chamber of a second cylinder where the compressed fluid is compressed to a second higher pressure before the fluid exits from an outlet of the compressor; wherein each piston is driven by one and the same crankpin of the compressor.
 57. A multi-stage compressor according to claim 56, further comprising at least one supply compressor for supplying compressed fluid at a pressure above atmospheric pressure to the compression chamber of the first cylinder, wherein the supply compressor and the pistons is driven by one and the same crankshaft as the pistons of the multi-stage compressor.
 58. A multi-stage compressor according to claim 57, wherein the at least one supply compressor is driven by the one and same crankpin as the pistons of the multi-stage compressor.
 59. A multi-stage compressor according to claim 56, wherein a separate and individual sliding shoe for engaging with the crankpin is attached to a bottom end of each piston.
 60. A multi-stage compressor according to claim 56, wherein a housing of the multi-stage compressor comprises at least one guide groove, the at least one guide groove being configured for guiding the movement of at least one guide element attached to a piston.
 61. A multi-stage compressor according to claim 56, wherein the multi-stage compressor comprises at least one linear bearing configured for guiding the movement of an associated piston of the pistons of the multi-stage compressor and/or at least one guide element attached to the associated piston.
 62. A multi-stage compressor according to claim 56, wherein the compression chamber of at least a first cylinder of the two or more cylinders is connected to the compression chamber of a second cylinder through at least one non-return valve for preventing flow of fluid from the compression chamber of the second cylinder to the compression chamber of the first cylinder.
 63. A multi-stage compressor according to claim 62, wherein the at least one non-return valve is located externally of the two or more cylinders inside a valve pipe such that a fluid flowing from the compression chamber of at least a first cylinder to the compression chamber of a second cylinder flows through the valve pipe and the at least one non-return valve.
 64. A multi-stage compressor according to claim 63, wherein the valve pipe is removably attached between two cylinders.
 65. A multi-stage compressor according to claim 63, wherein the valve pipe extends between a given cylinder and a directly following cylinder.
 66. A multi-stage compressor according to claim 56, wherein for at least one cylinder, a cylinder housing comprising the associated compression chamber of the given cylinder is detachable from and attachable to the compressor.
 67. A multi-stage compressor according to claim 59, wherein each sliding shoe is secured to the crankpin by an associated separate annular holding ring which encloses a circumference of the crankpin.
 68. A multi-stage compressor according to claim 59, wherein at least one sliding shoe comprises a recess or opening for receiving a holding ring.
 69. A multi-stage compressor according to claim 56, wherein the compressor is configured such that, in at least one of operation and at standstill, at least one or each piston do(es) substantially not touch an inner wall of the associated compression chamber.
 70. A multi-stage compressor according to claim 56, wherein the compressor is configured such that, in operation, at least one piston only or substantially only moves in the radial direction of the compressor.
 71. A multi-stage compressor according to claim 56, wherein the first cylinder comprises at least one associated rod seals for sealing against an associated piston of the first cylinder.
 72. A multi-stage compressor according to claim 56, wherein at least one of the crankpin and a crankpin bearing provided on the crankpin has an outer diameter that is at least 1.1 times a smallest and/or largest stroke length of each of the pistons.
 73. A multi-stage compressor according to claim 56, wherein a length of a lever arm acting on a rotation axis about which the crankpin rotates is equal to or less than 200% of a smallest and/or largest stroke length of each of the pistons.
 74. A method for compressing a fluid in a multi-stage compressor, the compressor comprising two or more cylinders, each cylinder having a compression chamber and a piston so that a fluid in each of the compression chambers is compressed by the associated piston, wherein the cylinders are connected in series such that a fluid entering an inlet of the compressor is compressed to a first pressure in the compression chamber of a first cylinder and, then, enters into the compression chamber of a second cylinder where the compressed fluid is compressed to a second higher pressure, and wherein each piston is driven by one and the same crankpin of the compressor.
 75. A system for compressing a fluid, the system comprising: a multi-stage compressor according to claim 56 and a second compressor configured to provide fluid at a pressure above atmospheric pressure to the inlet of at least one of the multi-stage compressor and the compression chamber of the first cylinder. 